Watercolor and Salt – Adventures in physical change and absorption

Objective: Provide students the opportunity to better understand the concepts of physical change and absorption through the use of watercolors and salt.

Project 1Watercolor techniques and physical changePreparation, Demonstration, and Procedure:Discuss, compare and contrast physical and chemical reactions and changes. (See vocabulary below for definitions).
Demonstrate watercolor techniques of wet-on-wet or float background in watercolor, then the watercolor/salt technique by sprinkling grains of salt into the wet paint. The students will see the salt absorb the water leaving the pigment behind (physical change).

Once the salt has dried, engage the students in conversation about the physical changes that take place for a second time when the salt dehydrates and re-crystallizes, leaving behind interesting patterns and visual textures in the dried watercolor.

Project 2
Watercolor/Salt relief painting

Preparation, Demonstration, and Procedure:Introduce students to absorption rates by discussing and demonstrating building up layers of salt on watercolor paper to create a three-dimensional watercolor project.

Part1 (dry paper)– Sprinkling with your fingertips, apply layers of salt to dry watercolor paper to create a miniature landscape of salt mountain chains and valleys. Saturate a paintbrush with a chosen color of watercolor. Between each layer of salt, carefully add drops of watercolor to the salt landscape. Direct students to pay attention to what happens with the watercolor. (You may choose to have them record their observations in their sketchbook/journal for future discussion.) The watercolor may sit on top of the salt for a period of time before it begins to hydrate the salt. Once the salt does begin to absorb the watercolor, initiate a conversation with students about what they observe. (Does the watercolor spread across the paper, or stay put under the salt?) Continue adding watercolors to the salt landscape until satisfied with the color combinations, etc. Set this painting aside to begin drying.

Part2 (wet paper)– Apply clean water to a new sheet of watercolor paper with a paintbrush. Begin layering the salt in the same way as the first technique. Between layers, drop watercolor onto the salt and gradually build it up to create mountains and valleys of salt. Again, direct students to pay attention to what happens with the watercolor. (This time the watercolor quickly absorbs into the salt. Why? Because the salt has been partially hydrated by the damp paper.) Another difference is that the watercolor spreads out from the base of the salt in random directions on the damp paper.
Continue adding watercolors to the salt landscape until satisfied with the color combinations, etc. Set it aside to dry.

Initiate a conversation with students about absorption observations and why the rates differ in the two different processes.

Once these relief paintings are dry, you can help to preserve them using one of these media: white glue, acrylic varnish. Either of these will work to help hold the salt in place on the paper as the salt does not absorb them.

Questions to help direct student reflections:

What happens when the salt is applied to dry paper and the watercolor is dropped on it?

Why do you think that happens?

What happens when the salt is applied to damp paper and the watercolor is dropped on it?

Why do you think that happens?

Why do you think the salt sticks together in the three-dimensional mountain forms you created when it is dry?

What happens when the salt mountains are too tall? Why do you think that happens?

Salt DOES dissolve in water. That doesn’t mean that a chemical change has taken place however. A chemical change is where bonds are broken and NEW BONDS FORM causing a rearrangement of atoms into new molecules. Dissolving is a physical process where the substance retains its own physical characteristics but just changes state or shape etc. When salt is put in water, the sodium and chloride atoms are pulled apart by the water. They disappear. But if the water is taken away, the sodium and chloride atoms rejoin with each other.
~Van Hoeck

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One thought on “Watercolor and Salt – Adventures in physical change and absorption”

Fun! I’m glad to know that this is in fact not a chemical reaction. When I do salt and watercolor resist with my elementary students and try to explain what happens I ask them what happens when they eat potato chips or popcorn- they get thirsty! And even though we live in Texas, I also tell them about how trucks put salt down on icy roads to help make them safer.